<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 200px;
            height: 200px;
            margin: 100px auto;
            background-color: #ccc;
        }
    </style>
</head>

<body>
    <div class="box">

    </div>
</body>
<script>
    var box = document.querySelector('.box');
    box.addEventListener('mousemove', function (e) {
        // console.log(e.pageX);
        // console.log(box.offsetLeft);
        console.log(e.pageX - box.offsetLeft);
        console.log(e.pageY - box.offsetTop)
    })
</script>

</html>